Evolution of the surface chemistry of hot dip galvanized Zn–Mg–Al and Zn coatings on steel during short term exposure to sodium chloride containing environments

• The atmospheric corrosion of Zn–Mg–Al and Zn coating is studied.
• Difference in the occurrence and evolution of corrosion products is observed.
• Rapid appearance of DLH layer on the surface of Zn–Mg–Al coating is found.
• Formed DLH possesses a temporary protective function to Zn–Mg–Al coating.

In the current study, the evolution of corrosion products on the surfaces of hot-dip galvanized Zn–Mg–Al and standard Zn coatings during short term exposure to standardized salt spray test was investigated by X-ray photoelectron spectroscopy. The obtained results demonstrated a rapid formation of double layered hydroxides (DLH) covering the surface of the Zn–Mg–Al coatings. The DLH surface layer was found to stabilize the surface pH and hinder further surface alkalization as observed for the Zn coatings and indicated by the occurrence of Na2CO3. As a consequence, the progress of Zn–Mg–Al corrosion was slowed down, but not completely stopped.